Experimental Study On Macroscopic And Microscopic Spray Characteristics Of Diesel/PODE_3-4 Blends

With the growing issues of global energy and environment,it has become urgent to look for the clean and highly efficient alternative fuel resources.One of the efficient ways to improve engine combustion and emission is adding a certain proportion of oxygenated biomass fuels or oxygenated additives in the diesel.As a new oxygenated fuel can be applied to diesel engine,polyoxymethylene dimethyl ethers(PODEn)has aroused increasingly more attention because of its highlight advantages such as high cetane number,oxygen content,solubility in diesel fuel and so on.Due to the fuel spray and atomization play a significance role in the improvement of the mixture formation and combustion peformance in engines,it is necessary to investigate the characteristics of diesel/PODE3-4 blends.Some experimental conclusions also provide for the valuable reference on the spray and atomization to select an acceptable alternative fuel for diesel engine.The experiment was conducted under the diesel fuel,PODE3-4,and two diesel blend fuels of 20%and 50%by volume fraction of PODE3-4.The trial platform was constructed to carry out a visual constant volume chamber and the high pressure common rail test bench.The high-speed photograph technique and laser particle analyzer were applied to systematically investigation on the effects of injection pressure(80?120?160 MPa),nozzle diameter(0.12?0.16?0.20 mm),ambient pressure(3?4?5 MPa),ambient temperature(3 00?400?500 K)and measurement position(the axial distance of the nozzle is 30?50?70 mm)on macroscopic(including spray pattern,concetration distribution,spray cone angle,spray tip penetration,spray velocity,spray area,spray volume and mass of entrained air)and microscopic(including Sauter mean diameter,volume representative diameter and droplet size distribution)spray characteristics of test fuel.The results of macroscopic spray characteristics showed that,increased fuel injection pressure led to the spray pattern of test fuel expanded,spray cone angle,penetration distance,spray area,spray volume and mass of entrained air increased in different degrees.And with the increment of nozzle diameter,over concetration region of spray subjective pattern got extend,spray cone angle,penetration distance,spray area,spray volume and mass of entrained air showed a tendency of increasing,respectively.Then,high concetration area of the spray concetration field got enlarged with the ambient pressure increased,also the increment of ambient pressure led to the decrease trends of the penetration distance,average spray velocity(axial direction),projected area and spray volume,as well as increases of the spray cone angle,average spray velocity(radial direction)and mass of entrained air.With the rise of ambient temperature,there was an extension of the low concetration scope for the spray distribution,the spray cone angle and average spray velocity(radial direction)could be sightly reduced,and the mass of entrained air had the trend to sharp decrease,on the contray,penetration distance,average spray velocity(axial direction),spray area,spray volume got to increace,respectively.Besides,the peformance of macroscopic spray characteristics was P100>P50>P20>P0 under the same experimental condition,this indicated that,Blended a certain proportion of PODE3-4 into diesel fuel,which was very conducive to improve atomization quality and air-fuel mixture compared to those of conventional diesel fuel.The results of microscopic spray characteristics indicated that,the Sauter mean diameter and volume representative diameter of fuels were decreased in different degrees with the injection pressure increased or nozzle diameter got smaller,and caused droplet size distribution shifted to smaller size.In addition,with the development of the fuel spray along the axis to down stream,the Sauter mean diameter of test fuels sightly decreased,Dv50 and Dv90 presented increased gradually,but Dv10 reversed a downward trend.PODE3-4 oxygenated fuels converged to smaller Sauter mean diameter and volume representative diameter,and a greater proportion of size distribution than those of diesel fuel.It can be concluded that the peformance of microscopic droplet size was P100<P50<P20<P0.This suggested that blended PODE3-4 to diesel fuel would be beneficial for enhancing the droplets breakup,collision and coalescence.